1. Field of the Invention
Embodiments of the present invention relate to head stack assemblies, hard disk drives having the same, and hard disk drive methods, and more particularly, to a head stack assembly which can compensate for an imbalance in the center of gravity of the head stack assembly when an imbalance value of the center of gravity, measured with respect to the rotational center of a pivot shaft, does not satisfy predetermined requisites. The imbalance in the center of gravity can be compensated by making the imbalance value not more than a reference value that satisfies the requisites.
2. Description of the Related Art
Hard disk drives are one of may types of memory devices that include electronic units and mechanical units for respectively converting a digital electronic pulse into/from a permanent magnetic field on a disk to record and reproduce data. As an example, hard disk drives have been widely used as auxiliary memory devices for computer systems because they can access a large amount of data at a high speed. In addition, compact hard disk drives having a diameter of 0.85 inches, similar to the size of a coin, have been recently developed for mobile phones. It is expected that hard disk drive application areas will continue to increase in the future.
As an example, the hard disk drive includes a disk for storing data, a spindle motor for rotating the disk, a head stack assembly (HSA) for recording and/or reading data to/from the disk while moving across the disk around a predetermined pivot shaft, a printed circuit board assembly (PCBA) for controlling the above-described parts, and a base for supporting these constituent parts.
FIG. 1 illustrates a conventional head stack assembly of a hard disk drive. Referring to FIG. 1, a head stack assembly 110 includes a magnetic head 112 for the recording and/or reproducing of data to/from the disk, an actuator arm 113, pivoting around a pivot shaft 116, to move across the disk so that the magnetic head 112 can access data on different portions of the disk, a pivot shaft holder 115 for rotatably supporting the pivot shaft 116, and a bobbin 117, extending from the pivot shaft holder 115 in an opposite direction as the actuator arm 113, and having VCM coil 118 wound therearound between magnets (not shown) of a voice coil motor (VCM, not shown). The actuator arm 113 may include a swing arm 113a, rotating around the pivot shaft 116 by the operation of the voice coil motor, and a suspension 113b having an end portion where the magnetic head 112 is attached.
The voice coil motor may be a sort of a drive motor for pivoting the actuator arm 113 to move the magnetic head 112 over a desired position on the disk, according to the Fleming's left hand rule, that is, the force generated when current is applied to a conductive body located in a magnetic field. As current is applied to the VCM coil 118, located between the magnets, a force is generated and applied to the bobbin 117 to pivot the same. Thus, as the actuator arm 113, extending from the pivot shaft holder 115 in an opposite direction as the bobbin 117, pivots, the magnetic head 112 supported at the end portion of the actuator arm 113 moves across a rotating disk to search tracks and access desired information.
One of the items to consider when the head stack assembly 110 is designed and manufactured is to match the centers of gravity of the head stack assembly 110 and the pivot shaft 116. To match the centers of gravity of the head stack assembly 110 and the pivot shaft 116 is important to enhance a position determination accuracy of the magnetic head 112. This becomes even more important because the capacities of a hard disk drives have been rapidly increasing with the recent implementation of high track per inch (TPI) requirements, as well as because hard disk drives are becoming widely used for apparatuses other than personal computers.
When the imbalance value of the center of gravity of the head stack assembly 110, with respect to the rotational center of the pivot shaft 116, does not satisfy predetermined requisites, a position error signal (PES) during the seek of the magnetic head 112 becomes affected upon generation of vibrations. Consequently, throughput efficiency in reading/writing from/to a hard disk drive is lowered. Thus, there is a need to minimize imbalances in the front/back and left/right directions of the center of gravity of the head stack assembly 110 to within in a controllable range.
Designing of a head stack assembly 110 may be performed through simulations to maintain an acceptable imbalance of the head stack assembly 110. As an example, Korean Patent Publication No. 2002-042423 discusses the attachment of a dummy weight to compensate for imbalances for a dipop version of a hard disk drive. Similarly, Korean Patent Publication No. 1998-084524 discusses the attachment of a dummy weight to compensate for imbalance due to the attachment/detachment of a detachable swing arm.
However, even when the imbalance value is designed to be close to “0” in actual implementations, including the above referenced conventional systems, when the center of gravity of an actual manufactured head stack assembly is measured using a balance measurer, the imbalance value of the center of gravity of the head stack assembly 110 is different from a designed value, in particular, the imbalance value frequently does not match the predetermined requisites. This difference is typically due to differing tolerances in respective parts or processes. Since the actually manufactured head stack assembly 110 frequently has an imbalance value different form the designed value, there is a limit to the compensating of the imbalance in the center of gravity before measuring the center of gravity of the actually manufactured head stack assembly 110. Thus, a variety of methods to reduce process tolerances during the manufacture of the head stack assembly 110 have been used. Nevertheless, when the center of gravity of the actually manufactured head stack assembly 110 is measured using the balance measurer, the imbalance value frequently exceeds the reference imbalance value. Further, when a vibration test is performed with respect to the actually manufactured head stack assembly 110, the throughput, having a strong correlation with the imbalance value, does not satisfy the predetermined requisites.
As described above, according to conventional operations, even when the head stack assembly is designed to have an imbalance value close to “0”, the imbalance value of the center of gravity of the actually manufactured head stack assembly exceeds the required reference imbalance value. Thus, in the hard disk drive having such a head stack assembly, the position error signal is frequently affected by vibrations, thereby remarkably lowering throughput efficiency of the hard disk.